1. Field of the Invention
The present invention relates to an air conditioning apparatus for an automotive vehicle, and more specifically to an air conditioning apparatus which can automatically control the amount of air blown by a blower fan.
2. Description of the Prior Art
In conventional air conditioning apparatus for an automotive vehicle, a room temperature sensor is provided for detecting temperature within a vehicle room; a difference between the detected room temperature and a target temperature (preset by a temperature setting switch provided within the vehicle room) is calculated; and the amount of air blown by a flower fan is automatically controlled on the basis of the difference in temperature between the two.
On the other hand, in the conventional air conditioning apparatus for an automotive vehicle, in general an external air introduction mode and an internal air recirculation mode can be selected according to the situation. In the external air introduction mode, air outside the vehicle is introduced by a flower fan into the vehicle room through a cowl box. In the internal air recirculation mode, air within the vehicle room is sucked by the flower fan and then blown again into the vehicle room. In the prior-art air conditioning apparatus, however, there exists a problem in that air suction noise in the internal air recirculation mode is higher than that in the external air introduction mode under the condition that the same amount of air is blown into the vehicle room through the blower fan. The reason is as follows: although the air suction noise is produced in both the external air introduction mode and the internal air recirculation mode whenever the blower fan is being rotated, since air is introduced from the outside in the case of the external air introduction mode, the air suction noise is reduced passing through some elements such as instrument panel, etc. before reaching the driver's ears. In contrast with this, since air is directly introduced from under the instrument panel in the case of the internal air recirculation mode, the air suction noise is not reduced by any other elements and directly reaches the driver's ears. The air suction noise increases with increasing amount of air blown by the blower fan.
In the prior-art air conditioning apparatus, however, since the amount of air introduced into the vehicle room by the blower fan is controlled in the same way in both the external air introduction mode and the internal air recirculation mode, there exists a problem in that the air suction noise by the blower fan increases abruptly whenever the external air introduction mode is switched to the internal air recirculation mode, thus allowing the driver and the passengers to feel unpleasant.